A GPS carrier-phase frequency transfer link along a baseline of 450 km has
been established and is characterized by comparing it to a phase-stabilized
optical fiber link of 920 km length, established between the two endpoints, the
Max-Planck-Institut f\"ur Quantenoptik in Garching and the
Physikalisch-Technische Bundesanstalt in Braunschweig. The characterization is
accomplished by comparing two active hydrogen masers operated at both
institutes. The masers serve as local oscillators and cancel out when the
double differences are calculated, such that they do not constitute a
limitation for the GPS link characterization. We achieve a frequency
instability of 3 x 10^(-13) in 30 s and 5 x 10^(-16) for long averaging times.
Frequency comparison results obtained via both links show no deviation larger
than the statistical uncertainty of 6 x 10^(-16). These results can be
interpreted as a successful cross-check of the measurement uncertainty of a
truly remote end fiber link.Comment: 14 pages, 6 figure